Many various devices are used to optically form a real image of an object, e.g. the concave mirror, pinhole lens, convex lens, graded refractive index lens, etc. However, except for the pinhole lens, the other devices have limited depth of field and require sufficient space to preclude their incorporation into small, integrated optical devices. Pinhole lenses that are smaller than those used to form images can form a diffraction pattern that uniquely represents an object without resembling the object. The pinhole lens can only form a real image or diffraction pattern in direct line with the object and only behind the lens from the object.
Whereas a pinhole lens functions by virtue of its limited aperture, a pinhead mirror functions by virtue of its limited extent. The present invention is a reflecting analog of the pinhole lens. For the lack of an accepted terminology for the present invention, "the pinhead mirror" "pinhead surface" etc. are used throughout the present specification. The pinhead mirror is therefore an optical mirror of a substantially point sized, flat, reflecting surface.